[llvm] r314934 - [LoopDeletion] Move deleteDeadLoop to to LoopUtils. NFC
Marcello Maggioni via llvm-commits
llvm-commits at lists.llvm.org
Wed Oct 4 14:54:08 PDT 2017
Hi,
Not right now in opensource, but I think the method was meant in the first place to be in that spot and nobody just got around doing it.
In this way will be available as a utility to opensource or private passes alike.
Marcello
> On Oct 4, 2017, at 2:13 PM, Davide Italiano via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>
> Thanks. Are you planning to introduce new consumers?
>
> On Wed, Oct 4, 2017 at 1:42 PM, Marcello Maggioni via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> Author: mggm
>> Date: Wed Oct 4 13:42:46 2017
>> New Revision: 314934
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=314934&view=rev
>> Log:
>> [LoopDeletion] Move deleteDeadLoop to to LoopUtils. NFC
>>
>> Modified:
>> llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
>> llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp
>> llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp
>>
>> Modified: llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h?rev=314934&r1=314933&r2=314934&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h (original)
>> +++ llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h Wed Oct 4 13:42:46 2017
>> @@ -439,6 +439,20 @@ bool hoistRegion(DomTreeNode *, AliasAna
>> TargetLibraryInfo *, Loop *, AliasSetTracker *,
>> LoopSafetyInfo *, OptimizationRemarkEmitter *ORE);
>>
>> +/// This function deletes dead loops. The caller of this function needs to
>> +/// guarantee that the loop is infact dead.
>> +/// The function requires a bunch or prerequisites to be present:
>> +/// - The loop needs to be in LCSSA form
>> +/// - The loop needs to have a Preheader
>> +/// - A unique dedicated exit block must exist
>> +///
>> +/// This also updates the relevant analysis information in \p DT, \p SE, and \p
>> +/// LI if pointers to those are provided.
>> +/// It also updates the loop PM if an updater struct is provided.
>> +
>> +void deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
>> + LoopInfo *LI);
>> +
>> /// \brief Try to promote memory values to scalars by sinking stores out of
>> /// the loop and moving loads to before the loop. We do this by looping over
>> /// the stores in the loop, looking for stores to Must pointers which are
>>
>> Modified: llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp?rev=314934&r1=314933&r2=314934&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Scalar/LoopDeletion.cpp Wed Oct 4 13:42:46 2017
>> @@ -30,21 +30,6 @@ using namespace llvm;
>>
>> STATISTIC(NumDeleted, "Number of loops deleted");
>>
>> -/// This function deletes dead loops. The caller of this function needs to
>> -/// guarantee that the loop is infact dead. Here we handle two kinds of dead
>> -/// loop. The first kind (\p isLoopDead) is where only invariant values from
>> -/// within the loop are used outside of it. The second kind (\p
>> -/// isLoopNeverExecuted) is where the loop is provably never executed. We can
>> -/// always remove never executed loops since they will not cause any difference
>> -/// to program behaviour.
>> -///
>> -/// This also updates the relevant analysis information in \p DT, \p SE, and \p
>> -/// LI. It also updates the loop PM if an updater struct is provided.
>> -// TODO: This function will be used by loop-simplifyCFG as well. So, move this
>> -// to LoopUtils.cpp
>> -static void deleteDeadLoop(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
>> - LoopInfo &LI);
>> -
>> enum class LoopDeletionResult {
>> Unmodified,
>> Modified,
>> @@ -183,7 +168,7 @@ static LoopDeletionResult deleteLoopIfDe
>> P->setIncomingValue(i, UndefValue::get(P->getType()));
>> BI++;
>> }
>> - deleteDeadLoop(L, DT, SE, LI);
>> + deleteDeadLoop(L, &DT, &SE, &LI);
>> ++NumDeleted;
>> return LoopDeletionResult::Deleted;
>> }
>> @@ -219,129 +204,12 @@ static LoopDeletionResult deleteLoopIfDe
>> }
>>
>> DEBUG(dbgs() << "Loop is invariant, delete it!");
>> - deleteDeadLoop(L, DT, SE, LI);
>> + deleteDeadLoop(L, &DT, &SE, &LI);
>> ++NumDeleted;
>>
>> return LoopDeletionResult::Deleted;
>> }
>>
>> -static void deleteDeadLoop(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
>> - LoopInfo &LI) {
>> - assert(L->isLCSSAForm(DT) && "Expected LCSSA!");
>> - auto *Preheader = L->getLoopPreheader();
>> - assert(Preheader && "Preheader should exist!");
>> -
>> - // Now that we know the removal is safe, remove the loop by changing the
>> - // branch from the preheader to go to the single exit block.
>> - //
>> - // Because we're deleting a large chunk of code at once, the sequence in which
>> - // we remove things is very important to avoid invalidation issues.
>> -
>> - // Tell ScalarEvolution that the loop is deleted. Do this before
>> - // deleting the loop so that ScalarEvolution can look at the loop
>> - // to determine what it needs to clean up.
>> - SE.forgetLoop(L);
>> -
>> - auto *ExitBlock = L->getUniqueExitBlock();
>> - assert(ExitBlock && "Should have a unique exit block!");
>> - assert(L->hasDedicatedExits() && "Loop should have dedicated exits!");
>> -
>> - auto *OldBr = dyn_cast<BranchInst>(Preheader->getTerminator());
>> - assert(OldBr && "Preheader must end with a branch");
>> - assert(OldBr->isUnconditional() && "Preheader must have a single successor");
>> - // Connect the preheader to the exit block. Keep the old edge to the header
>> - // around to perform the dominator tree update in two separate steps
>> - // -- #1 insertion of the edge preheader -> exit and #2 deletion of the edge
>> - // preheader -> header.
>> - //
>> - //
>> - // 0. Preheader 1. Preheader 2. Preheader
>> - // | | | |
>> - // V | V |
>> - // Header <--\ | Header <--\ | Header <--\
>> - // | | | | | | | | | | |
>> - // | V | | | V | | | V |
>> - // | Body --/ | | Body --/ | | Body --/
>> - // V V V V V
>> - // Exit Exit Exit
>> - //
>> - // By doing this is two separate steps we can perform the dominator tree
>> - // update without using the batch update API.
>> - //
>> - // Even when the loop is never executed, we cannot remove the edge from the
>> - // source block to the exit block. Consider the case where the unexecuted loop
>> - // branches back to an outer loop. If we deleted the loop and removed the edge
>> - // coming to this inner loop, this will break the outer loop structure (by
>> - // deleting the backedge of the outer loop). If the outer loop is indeed a
>> - // non-loop, it will be deleted in a future iteration of loop deletion pass.
>> - IRBuilder<> Builder(OldBr);
>> - Builder.CreateCondBr(Builder.getFalse(), L->getHeader(), ExitBlock);
>> - // Remove the old branch. The conditional branch becomes a new terminator.
>> - OldBr->eraseFromParent();
>> -
>> - // Update the dominator tree by informing it about the new edge from the
>> - // preheader to the exit.
>> - DT.insertEdge(Preheader, ExitBlock);
>> -
>> - // Rewrite phis in the exit block to get their inputs from the Preheader
>> - // instead of the exiting block.
>> - BasicBlock::iterator BI = ExitBlock->begin();
>> - while (PHINode *P = dyn_cast<PHINode>(BI)) {
>> - // Set the zero'th element of Phi to be from the preheader and remove all
>> - // other incoming values. Given the loop has dedicated exits, all other
>> - // incoming values must be from the exiting blocks.
>> - int PredIndex = 0;
>> - P->setIncomingBlock(PredIndex, Preheader);
>> - // Removes all incoming values from all other exiting blocks (including
>> - // duplicate values from an exiting block).
>> - // Nuke all entries except the zero'th entry which is the preheader entry.
>> - // NOTE! We need to remove Incoming Values in the reverse order as done
>> - // below, to keep the indices valid for deletion (removeIncomingValues
>> - // updates getNumIncomingValues and shifts all values down into the operand
>> - // being deleted).
>> - for (unsigned i = 0, e = P->getNumIncomingValues() - 1; i != e; ++i)
>> - P->removeIncomingValue(e-i, false);
>> -
>> - assert((P->getNumIncomingValues() == 1 &&
>> - P->getIncomingBlock(PredIndex) == Preheader) &&
>> - "Should have exactly one value and that's from the preheader!");
>> - ++BI;
>> - }
>> -
>> - // Disconnect the loop body by branching directly to its exit.
>> - Builder.SetInsertPoint(Preheader->getTerminator());
>> - Builder.CreateBr(ExitBlock);
>> - // Remove the old branch.
>> - Preheader->getTerminator()->eraseFromParent();
>> -
>> - // Inform the dominator tree about the removed edge.
>> - DT.deleteEdge(Preheader, L->getHeader());
>> -
>> - // Remove the block from the reference counting scheme, so that we can
>> - // delete it freely later.
>> - for (auto *Block : L->blocks())
>> - Block->dropAllReferences();
>> -
>> - // Erase the instructions and the blocks without having to worry
>> - // about ordering because we already dropped the references.
>> - // NOTE: This iteration is safe because erasing the block does not remove its
>> - // entry from the loop's block list. We do that in the next section.
>> - for (Loop::block_iterator LI = L->block_begin(), LE = L->block_end();
>> - LI != LE; ++LI)
>> - (*LI)->eraseFromParent();
>> -
>> - // Finally, the blocks from loopinfo. This has to happen late because
>> - // otherwise our loop iterators won't work.
>> -
>> - SmallPtrSet<BasicBlock *, 8> blocks;
>> - blocks.insert(L->block_begin(), L->block_end());
>> - for (BasicBlock *BB : blocks)
>> - LI.removeBlock(BB);
>> -
>> - // The last step is to update LoopInfo now that we've eliminated this loop.
>> - LI.erase(L);
>> -}
>> -
>> PreservedAnalyses LoopDeletionPass::run(Loop &L, LoopAnalysisManager &AM,
>> LoopStandardAnalysisResults &AR,
>> LPMUpdater &Updater) {
>>
>> Modified: llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp?rev=314934&r1=314933&r2=314934&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp (original)
>> +++ llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp Wed Oct 4 13:42:46 2017
>> @@ -1137,6 +1137,128 @@ llvm::collectChildrenInLoop(DomTreeNode
>> return Worklist;
>> }
>>
>> +void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT = nullptr,
>> + ScalarEvolution *SE = nullptr,
>> + LoopInfo *LI = nullptr) {
>> + assert(!DT || L->isLCSSAForm(*DT) && "Expected LCSSA!");
>> + auto *Preheader = L->getLoopPreheader();
>> + assert(Preheader && "Preheader should exist!");
>> +
>> + // Now that we know the removal is safe, remove the loop by changing the
>> + // branch from the preheader to go to the single exit block.
>> + //
>> + // Because we're deleting a large chunk of code at once, the sequence in which
>> + // we remove things is very important to avoid invalidation issues.
>> +
>> + // Tell ScalarEvolution that the loop is deleted. Do this before
>> + // deleting the loop so that ScalarEvolution can look at the loop
>> + // to determine what it needs to clean up.
>> + if (SE)
>> + SE->forgetLoop(L);
>> +
>> + auto *ExitBlock = L->getUniqueExitBlock();
>> + assert(ExitBlock && "Should have a unique exit block!");
>> + assert(L->hasDedicatedExits() && "Loop should have dedicated exits!");
>> +
>> + auto *OldBr = dyn_cast<BranchInst>(Preheader->getTerminator());
>> + assert(OldBr && "Preheader must end with a branch");
>> + assert(OldBr->isUnconditional() && "Preheader must have a single successor");
>> + // Connect the preheader to the exit block. Keep the old edge to the header
>> + // around to perform the dominator tree update in two separate steps
>> + // -- #1 insertion of the edge preheader -> exit and #2 deletion of the edge
>> + // preheader -> header.
>> + //
>> + //
>> + // 0. Preheader 1. Preheader 2. Preheader
>> + // | | | |
>> + // V | V |
>> + // Header <--\ | Header <--\ | Header <--\
>> + // | | | | | | | | | | |
>> + // | V | | | V | | | V |
>> + // | Body --/ | | Body --/ | | Body --/
>> + // V V V V V
>> + // Exit Exit Exit
>> + //
>> + // By doing this is two separate steps we can perform the dominator tree
>> + // update without using the batch update API.
>> + //
>> + // Even when the loop is never executed, we cannot remove the edge from the
>> + // source block to the exit block. Consider the case where the unexecuted loop
>> + // branches back to an outer loop. If we deleted the loop and removed the edge
>> + // coming to this inner loop, this will break the outer loop structure (by
>> + // deleting the backedge of the outer loop). If the outer loop is indeed a
>> + // non-loop, it will be deleted in a future iteration of loop deletion pass.
>> + IRBuilder<> Builder(OldBr);
>> + Builder.CreateCondBr(Builder.getFalse(), L->getHeader(), ExitBlock);
>> + // Remove the old branch. The conditional branch becomes a new terminator.
>> + OldBr->eraseFromParent();
>> +
>> + // Rewrite phis in the exit block to get their inputs from the Preheader
>> + // instead of the exiting block.
>> + BasicBlock::iterator BI = ExitBlock->begin();
>> + while (PHINode *P = dyn_cast<PHINode>(BI)) {
>> + // Set the zero'th element of Phi to be from the preheader and remove all
>> + // other incoming values. Given the loop has dedicated exits, all other
>> + // incoming values must be from the exiting blocks.
>> + int PredIndex = 0;
>> + P->setIncomingBlock(PredIndex, Preheader);
>> + // Removes all incoming values from all other exiting blocks (including
>> + // duplicate values from an exiting block).
>> + // Nuke all entries except the zero'th entry which is the preheader entry.
>> + // NOTE! We need to remove Incoming Values in the reverse order as done
>> + // below, to keep the indices valid for deletion (removeIncomingValues
>> + // updates getNumIncomingValues and shifts all values down into the operand
>> + // being deleted).
>> + for (unsigned i = 0, e = P->getNumIncomingValues() - 1; i != e; ++i)
>> + P->removeIncomingValue(e - i, false);
>> +
>> + assert((P->getNumIncomingValues() == 1 &&
>> + P->getIncomingBlock(PredIndex) == Preheader) &&
>> + "Should have exactly one value and that's from the preheader!");
>> + ++BI;
>> + }
>> +
>> + // Disconnect the loop body by branching directly to its exit.
>> + Builder.SetInsertPoint(Preheader->getTerminator());
>> + Builder.CreateBr(ExitBlock);
>> + // Remove the old branch.
>> + Preheader->getTerminator()->eraseFromParent();
>> +
>> + if (DT) {
>> + // Update the dominator tree by informing it about the new edge from the
>> + // preheader to the exit.
>> + DT->insertEdge(Preheader, ExitBlock);
>> + // Inform the dominator tree about the removed edge.
>> + DT->deleteEdge(Preheader, L->getHeader());
>> + }
>> +
>> + // Remove the block from the reference counting scheme, so that we can
>> + // delete it freely later.
>> + for (auto *Block : L->blocks())
>> + Block->dropAllReferences();
>> +
>> + if (LI) {
>> + // Erase the instructions and the blocks without having to worry
>> + // about ordering because we already dropped the references.
>> + // NOTE: This iteration is safe because erasing the block does not remove
>> + // its entry from the loop's block list. We do that in the next section.
>> + for (Loop::block_iterator LpI = L->block_begin(), LpE = L->block_end();
>> + LpI != LpE; ++LpI)
>> + (*LpI)->eraseFromParent();
>> +
>> + // Finally, the blocks from loopinfo. This has to happen late because
>> + // otherwise our loop iterators won't work.
>> +
>> + SmallPtrSet<BasicBlock *, 8> blocks;
>> + blocks.insert(L->block_begin(), L->block_end());
>> + for (BasicBlock *BB : blocks)
>> + LI->removeBlock(BB);
>> +
>> + // The last step is to update LoopInfo now that we've eliminated this loop.
>> + LI->erase(L);
>> + }
>> +}
>> +
>> /// Returns true if the instruction in a loop is guaranteed to execute at least
>> /// once.
>> bool llvm::isGuaranteedToExecute(const Instruction &Inst,
>>
>>
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>
>
>
> --
> Davide
>
> "There are no solved problems; there are only problems that are more
> or less solved" -- Henri Poincare
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